This invention relates to a wet type sliding apparatus, and more particularly, to a wet type sliding apparatus comprising a thrust bearing excellent in wear resistance which operates in the presence of a lubricating liquid (lubricating oil or lubricating water). As a wet type sliding apparatus comprising a thrust bearing which operates in the presence of a lubricating liquid, there are various ones used in a generator, a pump, a turbine, a compressor, a transmission and the like. This invention uses a thrust bearing having a specific sliding surface to improve such a wet type sliding apparatus.
Aromatic polyetherketone resins or polyarylene sulfide resins are engineering resins having excellent heat resistance, mechanical properties and wear resistance. However, when the aromatic polyetherketone resin or polyarylene sulfide resin per se has a high friction coefficient, the application thereof to the sliding member which is one of the constituents of a bearing is difficult, so that a sliding member having a low friction coefficient has heretofore been developed by using the aromatic polyetherketone resin as the base material and adding thereto a resin having a low friction coefficient such as a fluorocarbon polymer or the like. On the other hand, however, this development has resulted in a deterioration of wear resistance and mechanical strength because the fluorocarbon polymer is contained.
As a technique concerning these aromatic polyetherketone resin systems, there is known the technique disclosed in JP-A 58(1983)-160,346. In this prior art, as a sliding member of a dry type sliding apparatus in which no lubricating liquid is used, there is stated a resin composition comprising a thermoplastic aromatic polyetherketone resin as a base material, 2.5 to 60% by weight of a fluorocarbon polymer and 2.5 to 60% by weight of a carbon fiber. However, the composition range in which the practical heat distortion temperature (HDT) and limiting PV value have been actually confirmed is only 10 to 40% by weight of a fluorocarbon polymer (polytetrafluoroethylene) and 10 to 40% by weight of a carbon fiber. When a composition of 2% by weight of a fluorocarbon polymer and 18% by weight of a carbon fiber is used in the bearing of a copying machine, it has been confirmed that a creak is generated and the revolution becomes unusual (see Comparative Example 3 in the above prior art reference) and it is suggested that the amount of the fluorocarbon polymer becoming small is not desirable.
Recently, the area of the pad used in the thrust bearing which operates in the presence of a lubricating liquid and is incorporated into a generator or pump has been made small accompanying the tendency of miniaturization of apparatus, and a high specific load has come to apply to the pad. A thrust bearing applied under such severe conditions is required to have various properties such as high wear resistance and the like in addition to its excellent sliding characteristics under wet lubrication. In the case of, for example, a thrust bearing used in apparatus in which starting and stopping are repeatedly effected, only a small amount of a lubricating liquid is present at the time of starting, and hence, the thrust bearing is partially in solid contact with a counter member at the time of the starting, so that not only does a large starting power become necessary, but also, there is a fear that the sliding surface is damaged by the solid contact. Therefore, the thrust bearing is required to have, in addition to high wear resistance during operating, a small friction coefficient at the time of the starting and also have a high mechanical strength as well as excellent wear resistance. The wear resistance in the wet system should be such that the wear is 4 .mu.m or less, particularly 2 .mu.m or less, as determined by a change in thickness of test sample before and after a test in which a counter member is rotated for 30 seconds in an oil bath by, for example, a friction-wear tester and then rested for 300 seconds and this cycle is repeated 15 times (see Table 2 which appears hereinafter).
However, the wear resistance and mechanical strength stated about 10 to 40% by weight of a fluorocarbon polymer (polytetrafluoroethylene) and 10 to 40% by weight of a carbon fiber which are in the range of the best mode of the above-mentioned prior art relating to the dry type technique have not been sufficient. Moreover, as discussed above, in Comparative Example 3 of the above-mentioned prior art reference, it has been confirmed that when a composition consisting of 2% by weight of a fluorocarbon polymer and 18% by weight of a carbon fiber is used in the bearing of copying machine, a creak is generated and the rotation becomes unusual and it is stated that when the amount of the fluorocarbon polymer is 2% by weight, the composition is inappropriate as a sliding member. Furthermore, in the dry type prior art, when the amount of PTFE is less than 10% by weight, no sufficient lubricity is actually obtained.